The present invention relates to electric motors and more particularly to a mounting arrangement and coil retaining clip for a coil in an electric motor.
A standard electric motor is constructed of an annular stator surrounding a rotating armature or rotor whereby a plurality of windings on the rotor sequentially cut through lines of flux generated by magnetic poles established about the inner surface of the stator (field poles). In a direct current electric motor, the windings of the rotor are connected to a plurality of commutator bars and are supplied with power by brushes which rub against the bars to make an electrical contact. The currents through the armature windings on the rotor create magnetic poles on the rotor which interact with the flux generated by the magnetic poles of the stator to create torque on the rotor and cause rotation. The brushes force armature current reversal in each armature winding as the associated commutator bar passes under a brush. In order to prevent arcing at the brushes as the brushes pass from one commutator bar to another, motor designers typically provide commutating poles about the motor stator which cause a voltage to be generated to assist in reversing the current so that arcing at the commutator/brush interface is minimized.
Although the utilization of commutating poles within the motor solves the brush arcing problem, such poles create a construction problem in that the spacing between field poles and the windings on the field poles does not leave much room for insertion of additional windings about a commutating pole. In a typical motor construction process, an outer housing or stator shell is constructed of a magnetic material to provide a magnetic path for flux about the motor. Separate field and commutating poles are manufactured which can be bolted to the inside surface of the stator shell. The windings are wound outside of the motor and wrapped with appropriate insulation prior to installation. In the installation process, the pole faces are inserted through apertures in the center of the pre-formed windings and then bolted into position inside the stator. However, such a construction is not practical for smaller, lower horsepower motors. Preferably, in a lower horsepower motor, the field poles would be formed as an integral part of the stator shell and the windings thereafter either wound upon or placed upon the field poles. As long as there is sufficient space within the motor and between the field poles and adjacent windings, it is practical to wind the field poles in situ. Because the construction of most efficient types of main field poles requires that the surface of the pole adjacent the armature be as wide as possible, the typical construction requires a pole which is constructed with a shape in which the base of the pole adjacent the stator shell is narrower than the face of the pole adjacent the armature. Accordingly, for main field poles which are constructed as an integral part of the stator shell, it is not possible to pre-form the windings and place them over the poles. In such construction, it is usual to wind the field poles in situ. However, once the main field poles have been wound the space available within the stator shell for winding and commutating poles is such that economical winding of the commutating poles in situ is impractical. Fortunately, because the commutating poles are not required to have the same enlarged face configuration as main field poles, it is possible to pre-form windings which can be placed upon commutating poles that are made as an integral part of the stator shell.
Accordingly, it is an object of the present invention to provide a mounting arrangement for pre-formed windings in position around a pole in an electric motor.
It is a still further object of the present invention to provide an apparatus for holding pre-formed windings of an electric motor in place about a magnetic pole structure.
In accordance with the present invention, there is provided a mounting arrangement and apparatus for an electric motor which efficiently retains coils in place over a pole. In a preferred embodiment, the apparatus comprises a generally L-shaped member formed of stainless steel in which a first arm of the L-shaped member can be slipped between a pole and an inner surface or face of a winding placed around the pole. A second arm of the L-shaped member extends outwardly from the pole overlapping a portion of the winding. The first arm includes lance outs which slip into indentations in the sides of the pole and which are held in place by the pressure of the winding against the pole. The indentations prevent the L-shaped member from slipping out of the space between the winding and pole. Preferably the second arm of the L-shaped member forms an acute angle with the first arm to thereby provide a spring-like pressure against a surface of the winding to press the winding firmly against an inner surface of a stator shell. In addition, each of the distal ends of the L-shaped member include a reverse bend projecting away from an adjacent winding surface so as to prevent damaging of insulation on the winding. Each corner of the member is rounded with a large radius to eliminate high potential arc discharge points. In the mounting arrangement of a winding, a plurality of the L-shaped members may be utilized about a pole face in order to firmly secure a winding in position. The present invention thus provides a simple and economic means of securing a winding, such as a commutating winding, within an electric motor.